216 VISCERAL ANATOMY. 



What Nerves supply the Membrana Tympani ? The external layer 

 contains filaments from the Superficial Temporal branch of the 5th; the inner 

 layer is supplied by the Tympanic Plexus. (See Nerves of Tympanum.) 



THE TYMPANUM. 



Describe the Tympanum. The Tympanum, Drum, or Middle Ear, is 

 an irregularly-shaped cavity lying between the membrana tympani and the 

 internal ear, and communicating with the pharyngeal cavity by the Eustachian 

 tube. It contains the ossicles of the tympanum, part of the chorda tympani 

 nerve, and air. Its average diameters are about \ inch antero-posteriorly ? 

 \ to | inch vertically, and -jL to inch transversely. 



Name the Points on each wall of the Tympanum. Its 

 ROOF, is very thin, and corresponds to a depression on the anterior surface 



of the petrous portion of the temporal bone. 

 FLOOR, is a thin plate, separating it from the jugular fossa and vein. Has 



Opening for Jacobson 's Nerve, in the floor. 



OUTER WALL, is formed by the membrana tympani and presents the 

 Iter Chorda Posterius, opens close to posterior edge of drumhead, for the 



entrance of the chorda tympani nerve. 

 Iter Chorda Anterius, or Canal of Hugier, opening just in front of the 



drumhead, for the exit of the chorda tympani nerve. (See p. 16.) 

 Glaserian Fissure, opens above and in front of the drumhead, receiving 

 the long process of the malleus, the anterior ligament of the malleus, and 

 the tympanic artery. (See ante, p. 15.) 

 INNER WALL, is the outer wall of the labyrinth; presents the 



Fenestra Ovalis, an oval opening, leading into the vestibule, and closed 



by a membrane, to which is attached the base of the stapes. 

 Fenestra, Rotunda, a smaller opening, below the fenestra ovalis, leading 

 into the scala tympani of the cochlea, and closed by the Membrana Tym- 

 pani Secundaria. 

 Promonotory, an elevation corresponding to the first turn of the cochlea, 



situated between the fenestrse and in front of them. 

 Ridge of the Aqueductus Fallopii, above the fenestra ovalis, behind which 



it curves downwards along the posterior wall. 

 Pyramid, a conical eminence containing a canal which communicates with 



the aqueductus Fallopii and encloses the stapedius muscle. 

 ANTERIOR WALL, presents the 



Opening of Canal for the Tensor Tympani Muscle, above, situated on a 



small projection, the Anterior Pyramid. 



Opening of the Eustachian Tube, next below. These two canals being 

 separated by a bony lamina, the Septum Tuba. 



